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ABSTRACT: The objective of this study was to assess how long-term exposure to high glucose affects the α cell function and whether the increased glucagon secretion is mediated via insulin resistance.
We established a β cell-depleted rat model to obtain pure primary α cells. Furthermore, isolated rat islets and TC1-6 cells (a clonal α cell line) were exposed to high glucose (25 or 30 mmol/L) and low glucose (5.5 mmol/L) for up to 5 days to evaluate the influence of chronic glucose toxicity on glucagon secretion and glucagon gene expression. Moreover, we added insulin and/or Wortmannin to examine if the inhibitory effect of insulin on glucagon secretion was impaired by high glucose via the phosphatidylinositol 3 kinase/PKB protein kinase B pathway.
Both glucagon secretion and glucagon gene expression were increased in response to 5 days exposure to high glucose. While a moderate insulin concentration slightly inhibits glucagon secretion from rat islets and α TC1-6 cells at high glucose, a pronounced increase in glucagon secretion was observed at low glucose. We found that the insulin-mediated activity of the phosphatidylinositol 3 kinase/PKB protein kinase B pathway in the α cell was markedly impaired by chronic exposure to high glucose.
The hypersecretion of glucagon induced by glucotoxicity may be secondary to insulin resistance of the α cell induced by impaired activity of the insulin signaling pathway.
Endocrine Research 01/2012; 37(1):12-24. · 0.97 Impact Factor
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ABSTRACT: To study caspase-3 gene expression and [Ca(2+)]i homeostasis in verapamil (Ver)-induced human retinal pigment epithelium (RPE) cells apoptosis.
Ver 80mg/L was applied in cultured human RPE cells for 12, 24 and 48 hours to induce RPE cells apoptosis. The expression of apoptotic effector gene caspase-3 was assessed by reverse transcription polymerase chain reaction (RT-PCR). Single cell was measured using fluorescence indicator Fura-3/AM with MetaFluo4.5/coolsnapfx/IX70 intracellular Ca(2+) fluorescence imaging system.
High levels of expression of caspase-3 mRNA were observed in normal RPE cells and it significantly increased after co-cultured with Ver. The fluorescence in resting RPE cells was strong and distributed throughout the cells. The nucleus appeared more fluorescent than the cytoplasm. Calcium fluorescence of RPE cells attenuated after co-cultured with Ver.
Up-regulation of caspase-3 gene expression and disturbance of [Ca(2+)]i homeostasis might play pivotal roles in Ver-induced RPE cells apoptosis.
International Journal of Ophthalmology 01/2010; 3(4):288-90. · 0.04 Impact Factor
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ABSTRACT: To investigate the effects of reversal of hyperglycemic toxicity on the synthesis and secretion of glucagon by the alpha cells and the possible mechanisms thereof.
Mouse glucagonoma cells of the line TC1-6 were cultured in medium containing 5.5 mmol/L glucose for 10 days (low glucose group, LG), in medium containing 25 mmol/L glucose for 10 days (high glucose group, HG), in medium with 25 mmol/L glucose for 5 days and then in medium with 5.5 mmol/L glucose for 5 days (high-low glucose group, HL group), or in medium with 5.5 mmol/L glucose for 5 days and then in medium with 25 mmol/L glucose for 5 days (LH group), Radioimmunoassay was used to detect the glucagon concentration in the supernatant. RT-PCR was used to detect the mRNA expression of glucagon in the TC1-6 cells. Western blotting was used to detect the protein expression of the Snare proteins: syntaxin1A and synaptosome-associated protein (SNAP)-25.
(1) The glucagon level of the HG/LG group was lower than that of the HG group by 29% (P < 0.05). (2) The glucagon mRNA expression level in the TC1-6 cells of the HG/HL group was significantly lower than that of the HG group by (52.6 +/- 2.8)% (P < 0.05). (3) The syntaxin1A and SNAP-25 expression levels in the TC1-6 cells of the HG group were significantly higher than those of the LG group by 36% and 69% respectively (both P < 0.05), and the syntaxin1A and SNAP-25 expression levels in the TC1-6 cells of the HG/LG group were significantly lower than those of the HG group by 49% and 56% respectively (both P < 0.05).
After removing the high glucose toxicity the abnormal glucagon secretion by the alpha-cells can be ameliorated obviously, and the expression levels of syntaxin1A and SNAP-25 proteins that promote the secretion of glucagon are reduced accordingly.
Zhonghua yi xue za zhi 03/2009; 89(12):851-4.
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ABSTRACT: Isolated islets of Langerhans have been widely used to clarify the beta-cell function and insulin secretion in normal and diabetic states. Most of these studies have applied a pooled-islet design using isolated islets from a number of animals. However, to our knowledge, no previous studies have explored the consequences of using the pooled-islet design. From a statistical point, it may be preferable to use a design with islets from only one animal at a time under different experimental conditions and subsequently to repeat the experiments with islets from other animals. The present study compares these 2 designs in terms of their insulin response to glucose and arginine. We found higher insulin responses to glucose and arginine in pooled islets than in islets from individual animals, but differences between different stimuli were comparable between the 2 designs. However, the SEs on these differences are much smaller in the design with pooled islets than in the separate-islet design, and, consequently, corresponding P values will be much smaller. The statistical analysis of the design with islet separated per animal can explain this discrepancy because it identifies a non-ignorable random variation between animals compared with the variation within animals. In statistical terms, this implies a positive correlation between islets from the same animal. Ignoring this fact in the design with pooled islets overestimates the degrees of freedom and hence underestimates the SEs on the mean responses. This will in turn produce too small P values when using statistical tests to compare mean responses to different stimuli.
Metabolism 04/2007; 56(3):304-7. · 2.66 Impact Factor
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ABSTRACT: While the effect of fatty acids and ectopic triglyceride storage in pancreatic beta cells has been well-defined, only limited information is available on alpha cells. This study evaluates the long-term impact of fatty acids on alpha cell function and proliferation as well as fatty acid oxidation.
Clonal alpha cells were cultured with fatty acids in the presence of high glucose for up to 3 days. The influence of fatty acids on glucagon secretion, glucagon content and triglyceride accumulation from 24 to 72 h was investigated. After a - 72 h culture, cell proliferation, carnitine palmitoyl transferase-1 mRNA level and the effect of etomoxir were also elucidated.
Fatty acids stimulated glucagon secretion and increased triglyceride accumulation in a time- and dose-dependent manner, but inhibited alpha cell proliferation. Lower concentrations (0.125-0.25 mM) of fatty acids significantly increased glucagon secretion at 48 and 72 h, but did not affect triglyceride content. However, a marked increment in triglyceride accumulation occurred in the presence of 0.5 mM fatty acids. Fatty acids caused an up-regulation of the expression of carnitine palmitoyl transferase-1 gene. Etomoxir (1 microM) reversed fatty acid-induced glucagon hypersecretion, but did not inhibit carnitine palmitoyl transferase-1 mRNA level.
Our data indicates that compared with triglyceride accumulation, glucagon secretion is more sensitive to changes in fatty acid concentration. The effect of fatty acids on the glucagon response is mediated through their oxidation. The high carnitine palmitoyl transferase-1 gene expression and the accumulation of triglyceride may initially be a compensatory oxidation reaction to elevated fatty acids.
Diabetes/Metabolism Research and Reviews 04/2007; 23(3):202-10. · 3.37 Impact Factor
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ABSTRACT: The influence of fatty acids on beta cell function has been well established whereas little is known about the role of fatty acids on alpha cell function. The aim of our study was to investigate the short-term effects of chain length, spatial configuration, and degree of unsaturation of fatty acids on glucagon secretion from isolated mouse islets and alpha tumor cell 1 clone 6 cells (alpha TC1-6 cells). Glucagon release was measured with different saturated and unsaturated fatty acids as well as cis and trans isomers of fatty acids at low and high glucose. Palmitate (0.1-0.5 mmol/L) immediately stimulated glucagon release in a dose-dependent manner from both isolated islets and alpha TC 1-6 cells. The longer chain length of saturated fatty acids, the higher glucagon responses were obtained. The average fold increase in glucagon to saturated fatty acids (0.3 mmol/L) compared to control was octanoate 1.5, laurate 2.0, myristate 2.9, palmitate 5.4, and stearate 6.2, respectively. Saturated fatty acids were more effective than unsaturated fatty acids in stimulating glucagon secretion. At an equimolar concentration, trans-fatty acids were more potent than their cis isomers. Fatty acids immediately stimulate glucagon secretion from isolated mouse islets pancreatic alpha cells. The chain length, spatial configuration, and degree of unsaturation of fatty acids influence the glucagonotropic effect.
Metabolism 11/2005; 54(10):1329-36. · 2.66 Impact Factor
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ABSTRACT: To investigate whether insulin resistance is the common route for hereditary and environmental factors to cause hypertension.
93 hypertensives with family history of hypertension, 94 hypertensives without family history of hypertension and 99 normal tensives without family history of hypertension as well as their spouse, and one child in each family were enrolled in the present study. Insulin sensitivity was calculated from fasting plasma glucose (FPG) and insulin (FINS) with the formula insulin sensitivity index (ISI) = 1/(FPG x FINS) and insulin resistance index (Homa-IR) = (FPG x FINS)/22.5. The contribution of insulin resistance to blood pressure elevation was investigated by multivariate regression analysis.
Subjects with essential hypertension, regardless of the presence or absence of family history of hypertension, were more insulin resistant. Multivariate regression analysis demonstrated that insulin resistance contributed to 17% of mean blood pressure (MBP) elevation, whereas taken FPG + total cholesterol (TC) + high density lipoprotein (HDL) together it explained only 9% of MBP changes in the indicator group. When family history of hypertension was included as a independent variable in the analysis, it became the most important factor instead of insulin resistance in the model and contributed to 30% of the changes of MBP, while contribution of insulin resistance was significantly reduced as to explain only 7% of the changes of MBP.
Insulin resistance is a common route for hereditary and environmental factors to induce hypertension. It is suggested that improving insulin sensitivity may play an important role in the management of essential hypertension.
Zhonghua nei ke za zhi [Chinese journal of internal medicine] 02/2003; 42(1):11-5.
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ABSTRACT: To detect the association among calpain-10(CAPN-10) gene polymorphism, hypentension and hyperglycemia.
378 individuals in the present study were the second generation offsprings of 187 hypentensives and 19 1 nonhypertensives. Fasting plasma glucose (FPG), insulin, triglyceride and fibrinogen were determined. The polymorphism of UCSNP-43 and UCSNP-44 of CAPN 10 gene were analysed with PCR-SSCP method.
(1)The frequency of G/G geno type of UCSNP-43 was higher in the second generation offsprings of the hypertensives than that in the nonhypertensive controls(86.6%, 75.4%, P < 0.05). (2) The frequenncy of G/G genotype of UCSNP-43 was higher in the hypertensive parents of the second generation offsprings in the hypertensive groups than that in the normotensive parent of the second generation offsprings of the nonhypertensive control groups (OR = 2.84, P = 0.01). After adjustment of age, sex and body mass index (BMI), the frequency of G/G genotype in the highest FPG-quartiles (FPG 5.42 +/- 0.1mmol/L) was much more than that in the lowest FPG quartiles (FPG 4.09 +/- 0.3 mmol/L) with OR of 3.32.
Polymorphism of UCSNP-43 in CAPN-10 gene might be one of the genetic factors contributing to hypertension and diabetes mellitus in the population in Daqing city. It may be a predictor of type 2 diabetes mellitus (T2DM) in the decendents of hypertensives.
Zhonghua nei ke za zhi [Chinese journal of internal medicine] 06/2002; 41(6):370-3.
